1. Field of the Invention
The present invention relates to disc brake calipers and to improvements thereof. The present invention has particular relevance to disc brake calipers of the kind which include opposed pistons and it will therefore be convenient to describe the invention in relation to that type of caliper. It is to be appreciated however, that the invention could apply to calipers not of the opposed piston kind.
2. Description of Related Art
Opposed piston calipers have traditionally been applied to high performance vehicles, such as racing cars and top end sports cars. Such calipers have been perceived as providing higher performance than non-opposed piston calipers.
When used in high performance cars, the brake shoes of the caliper are supported on torque abutments positioned on the radially inward edge of the shoe (relative to the rotor), and a spring bias operates on the opposite or radially outer edge of the shoe to resist movement of the shoe away from one or each of the abutments during braking. The calipers are arranged in this manner, so that the brake shoes can be removed quickly after the spring or springs are removed, through an opening in the radially outer part of the caliper housing. However, the springs are required to be highly loaded to resist the signification loads applied by the brake shoes during braking. This does mean that the disassembly and reassembly of the caliper requires some expertise if it is to be done in a quick manner. This is one reason why the calipers have generally been used on high performance vehicles only.
Given the need for an opening in the housing for brake shoe removal, known opposed piston calipers such as those described above, have not been as stiff as desirable. Caliper stiffness is always a characteristic that is desirable to be maximised.
In known disc brake calipers friction lining wear tends to occur in a tapered manner, with the wear being maximum at the leading end of each shoe and tapering to minimum wear at the trailing ends. To eliminate or reduce the amount of tapering wear, ie to cause the friction lining to wear evenly or more evenly, some calipers have employed multiple pistons to drive the brake shoe, with a piston of greater diameter at the trailing end of the brake shoe compared to the leading end. Accordingly, greater pressure is applied to the brake shoe at the trailing end than the leading end, so having an evening effect on the friction lining wear. A drawback associated with this approach is that each caliper requires at least two different piston sizes and related seals and other parts, so complicating the manufacture and assembly process and therefore increasing costs.